Have you played any music on your iTunes, if not try, maybe you got the wrong version of iTunes, for Windows 7. There are a number of posts to address that problem.
If your iTunes runs normally, I can suggest that you disconnect from Internet, Stop your Antivirus program, then Restore/sync the Ipod.
Advisable to disconnect from Internet when you stop your Antivirus program, while syncing iPod.
I have found the only solution that works for me is to plug in the iPod and leave it until fully charged, then re-boot it with MENU+CENTRE after which Windows recognises it and stays connected.
I assume that the PC USB port can't supply enough power to charge the iPod battery and run its HDD at the same time - but that is just an assumption.
Hope this works for you.